1. Field of the Invention
The present invention relates to an ignition system for an internal combustion engine and, more particularly, an electronically controlled ignition system that includes a power switching element, an integrated control circuit (IC) and a protection circuit that protects the ignition system from extraneous electric surges.
2. Description of the Related Art
U.S. Pat. Nos. 5,483,093 and 5,668,384, which are based on JP-A-Hei 5-22099, disclose an ignition system that includes a power switching element, a control IC and a zener diode that protects the control IC from electric surges. The zener diode has a cathode connected to the input terminal of the control IC and an anode connected to a ground (GND). If a high frequency noise comes to the control IC, the zener diode removes it by its capacitance and voltage clamping function.
However, in order to substantially remove such high frequency noises that include noises of frequencies between 0.1 MHz and several tens of MHz, a discrete capacitor having much larger capacitor is necessary. Such a discrete capacitor increases the size and cost of the ignition system.